Friends,

I am new to GC and am having a difficult understanding what exactly goes on from the injector to the column in terms of flow and pressure control. From what I understand, ramping oven temp increases mobile phase viscosity and thus results in decreased flowrate. Therefore, to maintain constant flowrate through column, one must increase increase column headpressure to compensate and thus maintain constant flow. However, I read that split/splitless mode requires constant pressure. So the question becomes: How can you have constant flow (requiring increasing pressure) while at the same time do split/splitless (requiring constant pressure)? Also, why does split/splitless require constant pressure? What is the difference between EPC and manual pressure control? Is EPC and EFC the same? How does EPC work and where is the device located? Thank you for your help.

To fully explain everything would take a lot of time and space in this discussion group. I would suggest that you take one of the basic GC courses offered by a number of companies and organizations, for example Restek, the GC companies, ACS, MCF, etc. To get the fullest understanding of your specific GC the manufacturer's course would probably be the best, and likely the most expensive, option.

Briefly, there are several things in your question that are not really related. Injection mode and flow through the column are separate issues. You can have, and often do with modern instruments, constant head pressure during injection and ramped pressure during the analytical run.

There are various name for electronic flow control, but in essence they all function the same way and have most of the same capabilities from GC company to GC company.

Before you take a course get one of the fundamental books on the theory and practice of GC (Walt Jenning's books, as one example). Be careful when reading older books, as GC technology has seen some significant advances in recent years. I often here things stated as absolute fact that were true for one specific instrument 15 years ago, but are not generally applicable today.

I strongly suggest a course to get you up to speed quickly, plus at the course you have the opportunity to ask questions and get immediate follow-up if anything is not clear.